Heat transfer in a viscoelastic orifice flow at low to moderate Reynolds numbers

Direct numerical simulations of heat transfer in channel flows of a viscoelastic fluid with an immersed periodic rectangular orifice were carried out to investigate the statistics of the velocity and thermal fields. The friction Weissenberg number of the viscoelastic fluid was set at 20 and the Prandtl number was given as either 1.0 or 2.0. In the present flow configuration, the reduction rates of the drag factor and the Nusselt number were ranged in the percent drag reduction DR% = - 90%-20% and the percent heat-transfer reduction HTR% = 0%-50%, respectively. The variations observed in the Reynolds-number dependencies of DR%, HTR%, and the separated flow behind the orifice were analyzed. Consequently, the viscoelasticity was found to affect the orifice flow and its heat transfer most significantly in the transitional regime, since it suppressed the turbulent transition and/or the Kelvin-Helmholtz instability of the separated shear layer emanating from the orifice edge.